There is a growing need for personal protective apparel that guards against toxic chemical and biological agents. These agents may be                (a) accidentally released in a chemical manufacturing plant, in a scientific or medical laboratory or in a hospital;        (b) released intentionally during wartime by a government to attack the military forces of the opposition; or        (c) released during peacetime by criminal or terrorist organizations with the purpose of creating mayhem, fear and widespread destruction.        
For this reason, the United States military and other defense organizations of countries all over the world have sought to provide adequate protection against chemical and biological warfare agents. The need for such protective apparel also extends to police departments, fire departments, emergency responders and health care providers. These organizations are responsible for providing assistance and relief after a catastrophic release of chemical or biological toxins, but they cannot discharge their responsibilities without adequate protection (“Chemical Protective Clothing for Law Enforcement Patrol Officers and Emergency Medical Services when Responding to Terrorism with Chemical Weapons”, Arca, V. J. and Marshall, S. M., in report of the Chemical Weapons, Improved Response Program, U.S. Army Soldier and Biological Chemical Command, November 1999).
According to the Handbook of Chemical and Biological Warfare Agents (D. Hank Ellison, CRC Press, Boca Raton, Fla., 1st edition, 1999), most chemical warfare toxins are fatal at concentrations as low as 1 part per million (ppm). Hence, to provide adequate protection from chemical warfare agents, a protective suit has to be almost impermeable to such chemicals. It is not difficult to devise structures that are impermeable to toxic chemical vapors and liquids, but such structures are also hot, heavy and uncomfortable to wear. The degree of comfort offered by a protective suit is largely determined by the amount of water vapor that can permeate through the protective fabric. The human body continuously perspires water vapor as a method for controlling body temperature. When a protective fabric hinders the loss of water vapor from the body, the transpirational cooling process is hindered, which leads to personal discomfort. When a protective suit allows little or no loss of water vapor, extreme heat stress or heat stroke can result in a short period of time. Hence, in addition to offering the highest levels of protection against toxic chemicals and liquids, a practical chemical and biological protective suit must have high water vapor transmission rates. The appropriate protective structure must also be light in weight and offer the same high level of protection over a long period of time.
There is a large variety of protective apparel available in the market today. The garments that offer the highest levels of comfort (high water vapor transmission rates) offer little or no protection against chemical and biological hazards, while those that offer the highest levels of protection against toxic hazards are also typically impermeable to water vapor. For example, garments made from woven fabrics are very breathable and comfortable to wear but offer no protection from noxious agents. Nonwoven fabrics such as those sold under the trade name of Tyvek® spunbonded olefin (available from DuPont, Wilmington, Del.) offer protection from particulate agents but offer little protection against chemical liquids and vapors. These nonwoven fabrics are also less permeable to water vapor than woven fabrics made from natural or manmade fibers. Protective suits made from multiple layers of laminated polymer films offer high level of protection against both liquid and vapor agents but are also largely impermeable to water vapor. Such impermeable suits may require a Self Contained Breathing Apparatus (SCBA) to provide comfort to the individual wearing the protective suit.
Considerable effort has been expended in creating laminated multilayered film structures for chemical protective apparel. Each layer in the laminated structure is chosen to impart certain features to the apparel. Some layers provide strength, while others provide resistance to specific classes of chemicals. Such laminated structures may be characterized as passive structures because the barrier layers physically impede the motion of the toxic chemicals without necessarily interacting or reacting with the permeating chemical species. U.S. Pat. No. 4,772,510 (Mc Clure), U.S. Pat. No. 4,833,010 (Langley), U.S. Pat. No. 4,855,178 (Langley) and U.S. Pat. No. 5,626,947 (Hauer) describe various laminated structures consisting of one or more chemical barrier layers. Such laminated films significantly hinder the permeation of chemicals, but they also prevent transport of water vapor. Hence, apparel made from such multilayered films is exceedingly uncomfortable to wear.
Another example of a passive protective layer in apparel is the use of microporous membranes. The preparation and characteristics of microporous membranes are well known in the art—see, for example, Richard W. Baker, “Membrane Technology”, in Encyclopedia of Polymer Science and Technology, 3rd Edition, John Wiley & Sons, Hoboken, N.J., 2003, pages 184-248. Such membranes, depending on the pore size and the surface functionality of the pores, may provide protection against specific classes of liquid chemicals. Also, because of the porous structure, the membrane layer is more breathable and comfortable to wear than nonporous, multilayered laminated structures. U.S. Pat. No. 4,194,041 (Gore) describes the use of a hydrophobic microporous membrane made from either polytetrafluoroethylene or polypropylene in conjunction with a hydrophilic polymer layer as a water barrier. U.S. Pat. No. 5,260,360 (Mrozinski) describes a microporous membrane made from a polyolefin and a fluorochemical oxazolidinone. However, because the diameter of pores in such membranes typically ranges from 0.1 to 10 micrometers, the resulting structure cannot offer much protection against chemical vapors.
Research effort has also been directed towards creating protective apparel that is “reactive” in nature. The protective garment is made reactive by encapsulating certain chemical species into the garment that can absorb, adsorb or chemically react with toxic chemical vapors as they diffuse through the garment. Such reactive garments are usually made up of multiple layers wherein at least one layer comprises an encapsulated reactant, and at least one outer layer consists of an air permeable layer. U.S. Pat. No. 4,455,187 (von Blucher) describes the art of creating reactive garments by encapsulating the reactive species in an appropriate polymer and depositing the resulting solids onto a porous fabric. The reactive species suggested in the invention are silica xerogels, powdered metal oxides and hydroxides, molecular sieves, ion exchangers and various forms of activated carbon. U.S. Pat. No. 5,273,814 (Kelly) describes an improved reactive structure for chemical protection. The improvement is brought about by the use of a hydrophobic microporous membrane layer in conjunction with an activated carbon layer. The purpose of the microporous membrane is to provide protection from liquid chemicals and to protect the reactive layer from being inundated and poisoned by liquid chemicals. One of the major limitations of reactive garments is that they have a limited effective lifetime. This is because the reactive agents such as activated carbon do not just react with toxic chemical agents but can be poisoned by many different impurities in the environment. Thus, the level of protection offered by such reactive garments decreases with time. Also, reactive suits that rely on solid reactants such as activated carbon have significant weight and are therefore cumbersome to wear over long time periods.
Hazardous materials (“hazmat”) protective garments may also be created from semi-permeable or semi-selective polymer membranes. Such membranes are nonporous continuous polymer films usually prepared from polymer electrolytes and ion exchange polymers. Such selective membranes offer significant barrier to the permeation of chemical agents but still allow for the permeation of water vapor. U.S. Pat. No. 4,515,761 (Plotzker) describes the art of creating a composite protective fabric from a semipermeable polymer membrane, which is prepared from a highly fluorinated ion exchange polymer containing sulfonic acid metal ion salt functional groups. U.S. Pat. No. 6,579,948 (Tan) describes a method for creating protective semipermeable membranes from block copolymers of polystyrene and isobutylene, where a fraction of the styrene segments have been sulfonated to form sulfonic acid groups. The ionic content of the polymer allows for a greater transmission of water vapor than is possible for membranes made from non-sulfonated styrene block copolymers.
There are two major problems with all the protective garments described in prior art. First, all existing protective garments offer the same constant level of protection at all times. In most situations, the wearer of a protective garment does not require protection from the environment at all times. Protection is only needed when a toxic chemical or biological agent is present in the environment. Second, none of the garments described in the art offer an optimum balance of protection and comfort. In all cases described so far, either comfort is sacrificed at the expense of protection or vice versa. The object of this invention is to overcome the aforementioned problems using a membrane structure having movable membranes, one advantage of which is a variable and controllable permeability.